When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to selectively introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold via a controllable EGR valve. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
It is known that recirculation of exhaust gas into the fresh air stream generally increases the temperature of air charge entering the intake manifold, which under some engine operating conditions can frustrate the goals of an EGR system. Accordingly, some known EGR systems employ a conventional EGR cooler that is typically positioned in-line with the EGR conduit fluidly coupling the exhaust manifold to the intake manifold. Such EGR coolers effectively control the temperature of exhaust gas being introduced into the intake manifold.
It is desirable to monitor the operation of such EGR coolers to ensure proper operation and effectiveness of such EGR coolers. What is therefore needed is a system for monitoring the operation of an EGR cooler and diagnosing EGR cooler fouling conditions as they may occur.